1. Field of the Invention
The invention relates generally to harmonic drive gearing arrangements, and more particularly to a harmonic drive having output drives which can be adjusted while under power and rotating, for effecting tensional adjustments in a web of material being driven by the output.
2. Prior Art
Strain wave gearing, otherwise known as harmonic drive transmissions, is well known in the art as seen for example in U.S. Pat. No. 2,906,143 granted to Musser. A typical strain wave gearing comprises of a rigid circular spline, a flex spline disposed inside the circular spline, the flex spline being deformable into for example an elliptic configuration to bring the flex spline into engagement with the circular spline at 2 points and further have a number of teeth which is larger or smaller than the number of the circulus spline by two n, ("n" being a positive integer), and a wave generator disposed in the flex spline to deform the flex spline to for example an elliptic configuration so as to bring the flex spline into the engagement with the circulus spline at the two points on the major axis of the ellipsoid. The wave generator includes an elliptic cam plate and a ball bearing fittingly mounted on the outer periphery of the cam plate. The outer race of the bearing is inserted into the flex spline to deform the flex spline to the elliptic shape. In the strain wave gearing, as mentioned hear and about, the input shaft is fixed to the cam plate of the wave generator and rotated while the ellipsoid of the flex spline is rotated. Upon rotating the ellipsoid, one of the flex spline and the circulus spline is rotated relative to the other by amount that is in proportion to the difference in the number of teeth of the two splines. When an output shaft is mounted on either the flex spline or the circulus spline, the output shaft is rotated very slowly in comparison with the input shaft. Thus the strain wave gearing has frequently been applied to precision machinery, because in the gearing, a high reduction ratio is obtained in spite of a small number of elements used therefor.
There are harmonic drive mechanisms wherein drive members are external gears and are arranged at the center of the drive. The flexible member would thereby be an internal gear and the wave generator would be located on the outside of the drive. However, typically the drive cannot be adjusted by the external wave generator while the output drives are under power and located.
It is therefor an object of the present invention to overcome the disadvantages of the prior art.
It is a further object of the present invention, to provide a drive which may be adjusted by an external wave generator while the output drives are under power and rotating.